Allen and Peters • COMMON NIGHTHAWK NESTING BIOLOGY 
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50 m apart to minimize spatial autocorrelation. 
Points were not used if they were on a road or other 
airfield infrastructure, and were substituted with 
the next point on the list so there were five points 
completed for each plot. All random vegetation 
measurements were performed between 15 and 23 
June to coincide with the approximate midpoint 
of the grassland bird nesting season. Vegetation 
measurements were compared between years 
(2009 vs. 2010 nests), and between nests and 
random locations (2010 only) using nonparametric 
Wilcoxon rank sum tests (alpha = 0.05). 
Nesting Phenology .—We estimated the date of 
nest initiation (first egg laid) to assess nesting 
phenology for: ( 1 ) nests found during egg-laying 
iassuming 1 egg laid/day: Rust 1947), (2) nests at 
which the hatch date was known or could be 
estimated as the mid-point between two checks 
(assuming an 18-day incubation period: Brigham 
et al. 2011), and (3) nests found with young 
(estimated age based on photographs and field 
desenptions of known-age young; Brigham et al. 
2011; MCA, unpubl. data). These methods 
provide adequate accuracy for estimating nest 
initiation (Nur et al. 2004). We acknowledge that 
our sample is biased as it excludes nests that were 
found and failed during incubation (i.e., egg- 
candling or floatation were not used to assign eggs 
to age classes), and therefore represents a dis¬ 
proportionate number of successful nests. We 
explicitly tested whether daily nest survival rates 
varied over the course of the season to address this 
concern. 
RESULTS 
Nest Survival and Predation Rates—We found 
-0 nests during the 2 years of the study: nine in 
2009, and 11 in 2010. Four of the 20 nests (all 
from 2010 ) were excluded from nest survival 
a nalyses, including three found during the young 
s,a ge (i.e., post-hatching), and one found during 
the incubation stage that was inadvertently 
damaged by an observer during a check. We 
logged a total of 98 check intervals (median 
interval = 2 days) at the remaining 16 nests, 
yielding 224.5 exposure-days. 
13)111660 of 16 nests included in nest survival 
analyses survived to hatching, while three tailed, 
two due to predation, and one was abandoned. All 
three nest failures occurred in 2010. The aban¬ 
doned nest apparently had infertile eggs as 
incubation was undertaken lor at least 27 days. 
The daily nest survival rate for the 16 nests was 
0.987 (95% Cl = 0.960-0.996); thus there was 
-79% chance (95% Cl = 48-93%) of surviving 
an 18-day incubation period (calculated as [daily 
survival rate] 1 *). There was no evidence that 
daily nest survival rale varied over the course of 
the season (x = 1.1. df = L P = 0.29). The 
daily predation rate w-as 0.009, indicating there 
was a 15% chance of a nest being depredated 
during the 18-day incubation period (95% Cl — 
4-47%). 
Eggs in 16 nests successfully hatched (including 
those found after hatching), and fledging was 
confirmed at only three. It is unknown whether 
young from the remaining 13 nests were predated or 
we lost track of them due to movements of young. 
The young at one nest were likely depredated by a 
northern pine snake {Pimophis mektnoleucus mel- 
anoleucus) that was observed ~ 1 m from 0-3 day 
old young that were not re-located. 
Clutch Size and Movements of Young.—C lutch 
size was two at 16 of the 17 nests found prior to 
hatching with the other nest containing a single 
egg. All three nests found after hatching contained 
two young. 
We recorded movements of young at 11 of 12 
nests visited more than once. The one pair of 
young not observed to change locations was 
<5 days of age when last seen. Twenty-six 
movement events were observed in 42 post¬ 
hatching checks. Exact distances traveled were 
not uniformly recorded, but ranged during a 
single check interval (generally 2—3 days) from 
0.15 to 6 m. Younger chicks tended to move less. 
Young that moved w'ere generally located close 
together (within 0.1 m) except for those close to 
fledging, which wrere at times — 1-2 m apart. One 
of four broods visited on day of hatching had not 
moved by the following nest check (2-3 days 
later), and three broods had moved only 15- 
100 cm. The farthest straight-line distance 
recorded to the original nest site over the 14- 
day period one pair of young were monitored was 
—45 m. In contrast, a pair of 11-day old young at 
another nest moved only 0.5 m from the original 
nest site. 
Nest-site Characteristics and Habitat Selection— 
Nest sites in both 2009 and 2010 were dominated by 
open ground (mean ± SD cover. 58 ± 20%, range 
= 5-80%. n = 17), followed by grass (18 ± 11%, 
range = 5-35%). shrubs (9 ± 13%, range = 0- 
40%). and forbs (9 ± 15%, range = 0-45%). Mean 
vegetation height at nest sites wus 11 ± 7 cm (range 
= 0-50 cm). Vegetation characteristics at nests were 
